Technical Abstract:
Soybean rust (Phakopsora pachyrhizi Sydow), was introduced into the continental U.S. in November, 2004. The utilization of resistant cultivars may be the most sustainable means of disease control. Resistance has been identified but has not been durable. As part of the effort to identify new sources of resistance, experiments were conducted at the Plant Protection Research Institute (PPRI) and the USDA-ARS Foreign Disease-Weed Science Research Unit (FDWSRU) BSL-3 Plant Pathogen Containment Facility in Fort Detrick, MD. 57 soybean accessions, previously identified as resistant, were screened in the field at VASI during January through May 2005. Based upon the first evaluation, 39 of the accessions were subsequently evaluated in two consecutive seasons. Three accessions, PI 437323, PI 398998 and PI 459025B, with resistant reddish-brown lesions and low sporulation levels were identified. A fourth accession, PI549017, with a low number of tan lesions was also identified. Two accessions, PI 437323 and PI 398998, along with four accessions from Paraguay and nine cultivars from Vietnam that have been identified as containing rust resistance, accessions containing the known single rust resistance genes (Rpp1-4), and the susceptible cultivar Williams 82 were inoculated in seedling assays at the FDWSRU with each of ten soybean rust isolates. All accessions, but one, had a race specific response to one or more of the rust isolates. The exception was PI459025B (Rpp4), which was resistant to all rust isolates. The reactions of the accessions selected for resistance in this study differed from that of the four accessions with known genes, indicating that they may be potential sources of new resistance genes.